Use of dicyanamides in and with photosensitive systems

ABSTRACT

DICYANAMIDES ARE INCORPORATED IN OR EMPLOYED WITH SILVER PHOTOSENSITIVE SYSTEMS. DICYANAMIDES CAN BE INCORPORATED IN SILVER HALIDE DEVELOPING COMPOSITIONS TO PROVIDE GREATER COVERING POWER. THEY CAN BE EMPLOYED IN LOW SOLVENT DEVELOPING COMPOSITIONS TO ENABLE SUCH COMPOSITIONS TO BE USED IN SOLVENT TRANSFER PROCESSES. THE SILVER DICYANAMIDE COMPLEX IS LIGHT SENSITIVE AND CAN BE EMPLOYED ALONE OR IN COMBINATION WITH SILVER HALIDE IN PHOTOGRAPHIC EMULSIONS.

United States Patent 3,563,740 USE OF DICYANAMIDES IN AND WITH PHOTOSENSITIVE SYSTEMS Grant M. Haist, James R. King, and Lance H. Bassage,

Rochester, N.Y., assignors to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey No Drawing. Filed Sept. 28, 1967, Ser. No. 671,218 Int. Cl. G03c 5/54, 5/30, 1/76 US. C]. 96-29 17 Claims ABSTRACT OF THE DISCLOSURE This invention relates to photographic systems. In a particular aspect it relates to light-sensitive elements and methods of processing them.

Light-sensitive systems based on silver halides depend upon the development of exposed material to provide visible images. This development is characterized by the chemical reduction of an exposed silver salt to metallic silver using an appropriate reducing agent. Various addenda have been incorporated in silver halide emulsions and in developing compositions to enhance the development operation and the nature of the image. Although a large number of addenda are known and used to accomplish a wide variety of results, there is nevertheless a constant search for new addenda which can be used to give results superior to those which could be achieved with prior art addenda, or which will replace several prior art addenda with a single addendum, or which will accomplish the same results as prior art addenda more economically.

In addition to the silver systems which give a negative image, various processes have been devised for the formation of positive images. Included among these systems are those which are based on solvent transfer of unexposed and undeveloped silver salt from the film base to a receiving sheet whereat the salt is reduced to metallic silver to form a positive image.

For some time, and particularly in recent years, there has been a search to reduce the amount of expensive silver required to produce a given result. Of course, a compromise in quality is not acceptable. Rather, the reduction in silver usage must be the result of increased efiiciency through a catalytic or synergistic effect.

One object of this invention is to provide a new lightsensitive system which requires less silver for a given image density.

Another object of this invention is to provide a new development system for silver halide photographic elements.

Yet another object of this invention is to provide a novel system for preparing electrically conductive coatings by a photographic development process.

Still another object of this invention is to provide a new solvent transfer system.

Still another object of this invention is to provide a novel photosensitive element.

3,563,740 Patented Feb. 16, 1971 Other objects and advantages of this invention will become apparent to those skilled in the art from a consideration of the following description of the invention.

The instant invention is concerned with the interaction between the dicyanamide ion and photosensitive silver salts. In accordance with our invention dicyanamides are used in conjunction with systems containing light-sensitive silver compounds. The dicyanamide can be incorporated in the light-sensitive element, or it can be incorporated in developing compositions for photographic silver salt emulsions. Several advantageous efiects are to be gained from the use of dicyanamide ions in conjunction with silver photographic systems.

When dicyanamide ions are included as an additive in a developing composition, the form of the reduced silver is such as to provide greater covering power. Covering power is defined as the ratio, D/M, where D is optical density of the image and M is the mass of developed silver per unit area. Since the rate of development is substantially unchanged by the addition of dicyanamide ions, and since a given unit of silver reduced in the presence of such ions provides greater covering power, the effective rate of development is increased by the inclusion of dicyanamide ions in a developing solution, Alternatively, by developing an emulsion which contains less silver with a developing solution containing dicyanamide ions for a normal length of time, an image having contrast to be expected from an emulsion having a greater silver content is obtained.

Another advantage which results from including dicyanamide ions in developing compositions is that, by appropriate adjustment of pH, conducting silver images can be formed in the normally unexposed and undeveloped areas of the element at the same time as the exposed areas are being developed. The silver thus formed differs in appearance and structure from the silver in exposed image areas in that it is shiny metallic silver having a plate-like appearance under magnification. It conducts electricity more readily than the silver which is formed in exposed image areas and hence can be used as a base for the electroplating of metals, such as in the manufacture of printed circuits and the like.

Dicyanamide ions can also be included in developing compositions used in solvent or diffusion transfer processes. When the dicyanamide is so incorporated enhanced solubility of the silver salt and greater covering power are obtained, thus permitting the use of low solvent developing solutions, which otherwise would not be operative in solvent transfer processes.

In yet another embodiment of this invention the dicyanamide can be incorporated directly in a photographic emulsion. The photosensitive material in such emulsions can be a silver dicyanamide complex, or it can be a mixture of a silver halide and a silver dicyanamide complex. In either case, such systems can be developed more rapidly than if dicyanamide ions were absent from the emulsion. That is, for a given time of development, emulsions including the dicyanamide ions give a higher contrast and a greater density than systems from which dicyanamide ions are absent. In addition, emulsions which incorporate dicyanamide ions have a reduced tendency to fog and exhibit an improved image tone.

Dicyanamide ions can be introduced into the photographic systems of the invention by any organic or inorganic compound which is a ready source of dicyanamide ions, so long as the compound is sufficiently soluble in the developing solution and does not contain moieties which would otherwise interfere with the development process.

Typical dicyanamides which are useful in the practice of the present invention include sodium dicyanamide, potassium dicyanamide, lithium dicyanamide, ammonium dicyanamide, etc.

The dicyanamides useful in the practice of the present invention can be prepared by methods known in the art. For example, the dicyanamides can be prepared by the reaction of sodium cyanide with cyanogen, or by the reaction of sodium or calcium cyanamide, with cyanogen halide. These and other methods of preparation of dicyanamides are further described in U.S. Pat. 2,455,895 and in J. Am. Chem. Soc., 44, pp. 486509 (1922).

Although the mechanism by which the dicyanamide ions function in photographic systems is not completely understood, use of the dicyanamides in and with photographic systems produces useful results as indicated above. Thus, the dicyanamides can be incorporated in known silver halide developing compositions to produce images of higher density, or to produce normal images either with reduced development time or with lesser amounts of silver.

The dicyanamides of this invention can be used in a wide range of silver halide developing compositions. In such compositions any suitable silver halide developer can be employed. Suitable silver halide developers within the scope of the invention include polyhydroxybenzene developer or silver salt reducing agents such as catechol, pyrogallol, hydroquinone, alkyl substituted hydroquinones, e.g., t-butyl-hydroquinone, methylhydroquinone and dimethyl hydroquinone, chlorosubstituted hydroquinones, e.g., chlorohydroquinone and dichlorohydroquinone, alkoxysubstituted hydroquinones, e.g., methoxy or ethoxy hydroquinones, hydroxylamine developer agents such as hydroxylamine hydrochloride, aminophenol developer agents such as 2,4-diaminophenols, methylaminophenols, and acyl derivatives of p-aminophenol such as described in British Pat. 1,045,303, ascorbic acid and isoascorbic acid developer agents, pyrazolidone developer agents such as 1-phenyl-3-pyrazolidone, including those described in British Pat. 930,572.

Ordinary development activators can be employed in the developing compositions useful in this invention. These include the typical alkalis employed for activating developers such as alkali metal hydroxides, e.g., sodium hydroxide, potassium hydroxide, and lithium hydroxide, as well as alkali metal carbonates such as sodium carbonate. These can be employed in any concentration necessary to achieve the required alkalinity in accordance with usual practice, pHs of at least 9 being more generally used.

Various addenda, known to those skilled in the art, can be incorporated for their known effect in the developing compositions of the present invention. These include buffers antifoggants, preservatives, thickening agents, and the like.

The amount of dicyanamide incorporated in the developing composition can be varied over a wide range depending upon the desired result. Especially useful results are obtained when there is employed about 0.05 to about 2.0 moles of dicyanamide per liter of developing composition. We prefer that the developing composition contain between about 0.5 to about 1.0 moles of dicyanamide per liter.

Electrically conducting silver images can be formed in the unexposed and normally non-developed areas of the film by developing the film with developing compositions, such as those described above in which the dicyanamide has been incorporated and adjusting the pH of the solution to at least a pH 11.

Developing compositions useful for the preparation of positive silver images by a solvent or chemical transfer process can also be prepared by incorporating the dicyanamide in low solvent developing solutions which otherwise are not useful in solvent transfer processes. The low solvent developing compositions are based on the developing compositions described above. In the absence of dicyanamide ion, their solvent effect on silver halide is such that when used in solvent or chemical transfer procedures, sufiicient silver halide does not migrate to the receiving sheet to permit the formation of a satisfactory image. However, by incorporating dicyanamide ions in such developing compositions good positive images are obtained on the receiving sheet. While the reasons for this result are not completely understood, it is believed that this is the result of greater solubility of silver halide in the presence of dicyanamide ion.

Such transfer processes are well known in theart. Rott in U.S. Pat. 2,352,014 described such a transfer process for preparing reversal images. In the Rott process an exposed photographic silver halide emulsion is impregnated with a developer and pressed in contact with a receiving sheet in the presence of a silver halide solvent and a fogging agent. The undeveloped silver halide in the emulsion layer is transferred by means of the silver halide solvent to the receiving sheet, this transferred silver halide developing to silver to form a positive image on the receiving sheet. Other investigators in this field, such as Land, suggested the use of various specific fogging agents or nuclei that could be used in the reception layer to facilitate the formation of a silver image therein and the use of viscous processing materials to facilitate the utilization of processing materials in pods positioned between the light-sensitive negative layer and the reception layer. Reference is made to such Land patents as US. Pats. 2,543,181, 2,584,029 and 2,698,236 for suitable photographic silver halide transfer proceses in which the present silver halide solvents can be effectively utilized.

A wide variety of nuclei or silver halide precipitating agents can be utilized in the reception layers used in silver halide solvent transfer processes. Such nuclei are incorporated into conventional photographic organic hydrophiliccolloid layers and include such physical nuclei or chemical precipitants as:

(a) heavy metals, especially in colloidal form and salts of these metals,

(b) salts, the anions of which form silver salts less soluble than the silver halide of the photographic emulsion to be processed, and

(c) nondiifusing polymeric materials with functional groups capable of combining with and insolubilizing silver ions.

Typical useful silver precipitating agents include sulfides selenides, polysulfides, polyselenides, thiourea and its derivatives, mercaptans, stannous halides, silver, gold, platinum, palladium, mercury, colloidal silver, aminoguanidine sulfate, aminoguanidine carbonate, arsenous oxide, sodium stannite, substituted hydrazines, zanthates, and the like. Polyvinyl mercaptoacetate is an example of a suitable nondiifusing polymeric silver precipitant. Heavy metal sulfides such as lead, silver, zinc, aluminum, cadmium and bismuth sulfides are useful, particularly the sulfides of lead and zinc alone or in an admixture, or complex salts of these with thioacetamide, dithio-oxamide or dithio-biuret. The heavy metals and the noble metals particularly in colloidal form are especially effective. Other silver precipitating agents will occur to those skilled in the present art.

The temperatures which are normally employed in photographic processing can be employed with developing compositions in which the dicyanamide is incorporated. Processing can be carried out at ambient temperatures, such as between 20 C. and 30 C., and at elevated temperatures, such as above about 50 C., e.g., 50-90 C. Suitable temperatures can be determined by those skilled in the art.

The time of development can vary from a few seconds to an hour or more, depending upon the processing conditions and the desired image. The optimum time can be readily determined by those skilled in the art based on the element to be processed, the temperature of processing, the various addenda present in the processing compositions, etc.

The developing compositions containing dicyanamides of the present invention are suitable for the development of a wide variety of photographic emulsions, particularly photo-graphic gelatino silver halide emulsions. Various silver salts can be used as the light sensitive component of the element. These include silver halides such as silver iodide, silver bromide, silver chloride, and mixtures of these silver halides. The photographic emulsions can be X-ray or other non-spectrally sensitized emulsions, or they can contain spectral sensitizing dyes, such as cya nines, merocyanines, styryls and hemicyanines. The photographic emulsions can contain various photographic addenda known to those skilled in the art. These include coating aids, plasticizers, hardeners, speed-increasing addenda, and the like.

The photographic elements processed according to the invention typically contain an emulsion layer comprising any of the known hydrophilic water permeable binders suitable for photographic purposes. These include, for example, gelatin, cellulose derivatives, polymerized vinyl compounds, as well as mixtures of such binding agents. These binding agents can also contain water insoluble materials such as water insoluble acrylate and methacrylate polymers.

The photosensitive coatings processed according to the invention can be coated on a wide variety of supports. Typical supports include cellulose ester films, such as cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate; polyester films such as polyethylene terephthalate; and, related films and resinous materials as well as glass, metals, papers such as polyethylene coated paper, and the like.

[In addition to incorporating the dicyanamide in silver halide developing compositions, useful effects are obtained when the dicyanamide is incorporated directly in a photographic emulsion. The dicyanamide is incorporated in the emulsion preferably as a complex with silver.

The silver dicyanamide complex can be prepared by reacting a dicyanamide with a soluble silver salt, e.g., inorganic silver salts such as silver nitrate or organic silver salts such as p-toluene sulfonic acid silver salt. This complex can be prepared prior to its incorporation into the emulsion or it can be formed directly in the emulsion by adding the reactive components to a suitable emulsion binder.

Since the silver dicyanamide complex is itself light sensitive, it can be the sole light-sensitive component in the emulsion. Alternatively, it can be present in the emulsion with other light-sensitive silver salts, such as silver halides, e.g., silver chloride, silver bromide, silver iodide and mixtures of these silver halides. Elements containing these light-sensitive components can be prepared by techniques well known to those skilled in the art.

In the elements of this invention the silver dicyanamide complex and the silver dicyanamide-silver halide mixture can be carried in a hydrophilic binder such as is used in silver halide emulsions. The elements of this invention also generally include a support material on which the emulsion is carried. Typical binders and support materials are described above in connection with the discussion of light-sensitive elements which can be employed with the novel developing compositions of this invention.

The amount of silver dicyanamide complex present in the photosensitive emulsion can be varied over a wide range depending upon its intended use and the conditions under which it will be exposed and developed. Typi cally, useful photosensitive elements can be obtained with amounts of silver dicyanamide ranging from 0.05 gram to 1.0 gram per gram of binder. Within this range amounts of silver dicyanamide of from 0.1 gram to 0.5 gram are preferred. However, these proportions are not intended to be limiting, and it should be understood that,

depending upon the particular use to which the element containing the silver dicyanamide complex is put and the conditions under which it is exposed and developed, equivalent results may be obtained using greater or lesser amounts of the silver dicyanamide complex. When the photosensitive emulsion contains silver halide in addition to the silver dicyanamide complex, up to mole percent of the silver dicyanamide can be replaced with silver halide and the emulsion will still have the useful properties associated with the presence of the dicyanamide lOIl.

The elements of this invention can be exposed and developed for lengths of time and by procedures known to those skilled in the art and generally applicable to silver halide elements. Known silver halide developing compositions, such as those described above, can be employed to develop the elements of this invention. In addition, the novel developing compositions containing dicyanamide ions, described above, can be employed for the development of these elements.

Emulsions containing the silver dicyanamide complex exhibit higher density and reduced fog than do ordinary silver halide emulsions processed under the same conditions. These emulsions can be used in positive-negative type films or in positive-positive solvent or chemical transfer films. Because of the enhanced solubility obtained by the presence of the dicyanamide in the emulsion, solvent or chemical transfer elements prepared from emulsions containing the silver dicyanamide complex can be processed with known low solvent developing solutions which normally would not give satisfactory results if used with emulsions not containing the silver dicyanamide complex.

This invention is further illustrated by the following examples.

EXAMPLE 1 Increased covering power of developed silver A developing solution was prepared having the following formulation:

Monomethyl-p-aminophenol sulfate-2.0 g. Sodium sulfite (desiccated)l00.0 g. Hydroquinone5.0 g.

Borax (granular)2.0 g.

Water to make-l liter Sodium dicyanamide was added to individual portion of this developing solution so as to give solutions having a concentration of sodium dicyanamide of 10, 20, 40, 60, and 80 g. per liter. Six strips of a medium speed negative film containing a gelatino silver halide layer were exposed behind a neutral density step wedge. Individual exposed Strips were then developed for 8 minutes at 68 F. in the unmodified developing solution and in each of the developing solutions which had sodium dicyanamide added. The strips were then fixed, washed and dried. The addition of increasing amounts of sodium dicyanamide to the solution resulted in progressive increases in both speed and gamma. The film developed in the solution containing 80 g. per liter of sodium dicyanamide had a gamma of 0.94, while the film developed in the unmodified solution had a gamma of 0.57. Using the solution containing 80 g. per liter of sodium dicyanamide resulted in a speed increase of 0.12 log E (measured at 0.1 density above fog) over the unmodified solution. Silver analysi indicated that in the areas receiving greater exposure there was less silver formed with the solution incorporating the dicyanamide than with the unmodified solution. Electron micrographs (40,000 of the developed silver images revealed that the increased covering power of the silver image produced by the solution containing the dicyanamide was the result of formation of very long silver filaments that were loosely grouped, while the unmodified solution formed shorter filaments which were much more compacted.

7 EXAMPLE 2 Formation of electrically conducting silver images A gelatino silver chloride emulsion on a paper support was imagewise exposed and then processed for 60 seconds at 75 F. in the following developing solution at pH 13.5

Hydroxylamine hydrochloride-20.0 g.

Sodium dicyanamide60.0 g. \-methylbenzotriazole (1% in 3A alcohol)-- ml. Sodium hydroxide30.0 g.

Water to make--1 liter.

After this 60 second immersion the print wa allowed to dry in the air. An electrically conducting silver image was formed in the normally undeveloped areas.

EXAMPLE 3 Formation of electrically conducting silver images A gelatino silver chloride emulsion on a paper support was imagewise exposed and then developed for 60 seconds at 75 F. in the following developing solution at pH 13.7:

l-phenyl-3-pyrazolidone3.0 g. Hydroquinone--l0.0 g.

Sodium sulfite (anhydrous)100.0 g.

Sodium dicyanamide-60.0 g.

Sodium hydroxide25.0 g.

5 methylbenzotriazole (1% in 3A alcohol)50 ml. Water to make-1 liter.

After processing for 60 seconds the print was allowed to dry in the air. An electrically conducting silver image was formed in the normally undeveloped areas.

EXAMPLE 4 Solvent transfer A gelatino silver chloride emulsion on a polyethylenecoated paper support was imagewise exposed and then immersed for 2 seconds in the following solution:

Monomethyl'p-a'minophenol sulfate-2.0 g. Hydroquinone3.0 g.

Sodium isoascorbate20.0 g.

Trisodium phosphate40.0 g.

Water to make-1 liter.

The negative was then pressed in contact with a solvent transfer receiving sheet containing nickel sulfied nuclei in a gelatin binder. After contact for 60 seconds the two sheets were stripped apart. There was no visible image transfered to the receiver. This procedure was repeated except that the developing solution contained g. per liter of sodium dicyanamide. A transferred positive silver image was obtained on the receiving sheet. When the solution contained 40 g. per liter of sodium dicyanamide, an image of higher density was obtained.

EXAMPLE 5 Solvent transfer A gelatino silver chloride emulsion on a polyethylene coated paper was imagewise exposed and then immersed for 2 seconds at room temperature in the'following solution:

Methyl-p-aminophenol sulfate-2.0 g. Hydroquinone3.0 g.

Sodium isoascorbate20.0 g. Trisodium phosphate40.0 g. Potassium dicyanamide20.0 g. Water to make-1 liter The negative was then pressed in contact with a nucleated receiving sheet as used in Example 4 for 60 seconds at room temperature and then the two sheets were stripped apart. A warm toned positive image was obtained on the receiving sheet. A transfer image with higher density was obtained when'40 g. per liter of potassium dicyanamide was present in the developing solution.

EXAMPLE 6 Light-sensitive silver complexes A light-sensitive coating was prepared in the following manner:

Part A:

20 ml. water 089 g. sodium dicyanamide Part B:

20 ml. water 0.84 g. silver nitrate Part C:

40 ml. 15% purified pigskin gelatin Part D:

0.5 g. p-toluenesulfonic acid The above solutions were maintained at F. Parts A and B were added slowly and simultaneously to Part C with continuous agitation. Then Part D was added to Part C and stirring was continued until the p-toluenesulfonic acid was dissolved. Thi mix was then coated at .006 inch wet thickness on a baryta coated paper base and was dried. The coated element was then given a sensitometric exposure. The exposed element was developed for 10 seconds at 75 F. in the following developing solution:

Monomethyl-p-aminophenol sulfate3.0 g. Sodium sulfite (desiccated)45 .0 g. Hydroquinone12.0 g.

Sodium carbonate- H O80.0 g.

Potassium bro.mide-2.0 g.

Water to make2 liters It was then stopped, fixed and washed. A developed image of moderate density and low fog was obtained.

EXAMPLE 7.

Light-sensitive silver complexes A light-sensitive coating was prepared in the following manner: Part A:

20 ml. of water 0.89 g. sodium dicyanamide Part B:

20 ml. water 1.39 g. p-toluenesulfonic acid, silver salt Part C:

40 ml. 15 pigskin gelatin Parts A and B were added slowly and simultaneously to Part C, while Part C was continuously agitated. All solutions were maintained at 110 F. This mixture was then coated at .006 inch wet thickness on baryta coated paper base and was dried in the air. A strip of this coated element was then sensitometrically exposed for 30 seconds. The exposed element was developed for 10 seconds at 75 F. in the developing solution of Example 6. The element was then stopped, fixed and washed. A neutral tone image of moderate density and low fog was obtained.

EXAMPLE 8 Image transfer from silver complexes A coated element was prepared and exposed as described in Example 7. The exposed element and a strip of a nucleated receiver sheet as used in Example 4 were soaked for 2 seconds in the developing solution of Example 6. The two strips were then brought into contact. After 60 seconds they were stripped apart and a positive image of warm brown tone was obtained on the nucleated receiver sheet.

9 EXAMPLE 9 Light-sensitive complexes containing a lower proportion of silver A light-sensitive coating was prepared in the following manner:

Part A:

20 ml. water 0.8 g. sodium dicyanamide Part B:

20 ml. water 0.25 g. silver nitrate Part C:

40 ml. 10% purified pigskin gelatin All solutions were maintained at 110 F. and Parts A and B were added slowly and simultaneously to Part C, while Part C was continuously agitated. This mixture was then coated at .006 inch wet thickness on a paper support. The coatings were allowed to dry at room temperature in the air. Photographic exposure and development were as in Example 7. There was obtained an image of moderate density and of lower fog level than in the coatings of Example 7.

EXAMPLE 10 Light-sensitive elements combining silver dicyanamide and silver halide A light-sensitive coating was prepared in the following manner:

Part A:

ml. water 0.25 g. silver nitrate Part B:

20 ml. water 0.8 g. silver dicyanamide Part C:

40 ml. 10% purified pigskin gelatin All solutions were maintained at 110 F. and Parts A and B were added slowly and simultaneously to Part C, while maintaining constant stirring. This mixture was then mixed with 2.2 ml. of a silver chloride emulsion prepared by mixing silver nitrate and potassium chloride in a gelatin solution. Photosensitive elements were prepared by coating strips of baryta-coated photographic paper support at a wet thickness of .006 inch with the silver dicyanamide-silver halide mixture and as a control with the unmodified silver chloride emulsion. These strips were then exposed to a 0.15 density step wedge and processed for 20 seconds in the developing solution of Example 6. The coated element which contained the dicyanamide and the silver chloride produced a higher contrast and a higher maximum density for a given time of development than the element which was coated only with the silver chloride emulsion. Further, the image tone of the control coating was less black than the image tone produced by the light-sensitive coating containing the dicyanamide.

EXAMPLE l1 Light-sensitive silver complex A light-sensitive coating was prepared in the following manner:

Part A:

40 ml. distilled water 1.78 g. sodium dicyanamide Part B:

40 ml. distilled water 0.85 g. silver nitrate Part C:

80 ml. 10% pigskin gelatin Part C was maintained at F. Parts A and B were added slowly and simultaneously to Part C with continuous stirring. This emulsion was then divided into two portions. A small quantity of a spreading agent was then added to one portion of the emulsion and it was coated on baryta-coated paper base at a wet thickness of .006 inch. The second portion was chill set, out into noodles, and washed for 1 hour in running tap water at 40 F. Coatings were then made in the same manner as above using this washed emulsion. When dried all coatings were given sensitometric exposures and developed for 16 seconds at 68 F. in the developing solution of Example 6. They were then stopped, fixed and washed. The coatings prepared from the washed emulsion composition produced images which were more free of fog than the coatings that were not washed.

The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined in the appended claims.

We claim:

1. A photographic silver salt developing composition comprising a developer agent and a dicyanamide.

2. A photographic silver salt developing solution containing the developing composition of claim 1 wherein the dicyanamide is present in amounts of from 0.05 to 2.0 moles per liter of solution.

3. A developing composition as defined in claim 1 wherein the dicyanamide is selected from the group consisting of sodium dicyanamide, potassium dicyanamide, lithium dicyanamide and ammonium dicyanamide.

4. A photographic silver salt developing solution comprising a developer agent and from 0.5 to 1.0 moles of sodium dicyanamide per liter of solution.

5. A photographic silver halide developing solution comprising an aqueous solution of a silver halide developer agent and a dicyanamide selected from the group consisting of sodium dicyanamide, potassium dicyanamide, lithium dicyanamide and ammonium dicyanamide present in amount of from 0.05 to 2.0 moles er liter of solution.

6. A photographic element comprising a support and a photosensitive emulsion, said emulsion containing a silver soluble dicyanamide salt complex formed by reacting a dicyanamide with a soluble silver salt.

7. An element as defined in claim 6 wherein the emulsion contains silver halide as an additional light-sensitive component.

8. A process which comprises developing an exposed photographic emulsion containing a light-sensitive silver compound in the presence of dicyanamide ions.

9. A process as defined in claim 8 wherein the dicyanamide ions are present in the photographic emulsion.

10. A process as defined in claim 8 wherein the emulsion is developed by contacting it with a developing solution containing a developer agent and dicyanamide ions.

11. A process as defined in claim 10 wherein the photographic emulsion is a light-sensitive silver halide emulsion.

12. A process as defined in claim 11 wherein the pH of the developing solution is at least pH 11, thereby forming a conducting silver layer in the unexposed areas of the emulsion.

13. A process as defined in claim 11 wherein the dicyanamide ions are introduced into the developing solution by a soluble dicyanamide salt selected from the group consisting of sodium dicyanamide, potassium dicyanamide, lithium dicyanamide and ammonium dicyanamide.

14. A process as defined in claim 13 wherein the amount of dicyanamide salt present in the developing solution is between 0.05 and 2.0 moles per liter of solution.

15. A photographic solvent transfer method for processing an exposed silver salt emulsion which comprises developing the exposed silver salt with a developing solution 1 1 12 to produce a negative silver image, transferring unexposed R f re Cited and undeveloped silver salt to a receiving sheet and reduc- UNITED STATES PATENTS ing the transferred silver salt to silver, the process being carried out in the presence of dicyanamide ions. 2455895 12/ 1948 Nagy 2378 16. A process as defined in claim 15 wherein the de- 5 3,259,497 7/ 1966 Wartburg 95-53 veloping solution contains between 0.05 and 2.0 moles of dicyanamide per liter of Solution NORMAN G. TORCHIN, Primary Examiner 17. A process as defined in claim 16 wherein the di- M. F. KELLEY, Assistant Examiner cyanamide is selected from the group consisting of sodium dicyanarnide, potassium dicyanarnide, lithium dicyanamide l0 and ammonium dicyanamide. 96 66J 7 94 114 

